<script setup>
import { onMounted, watch, nextTick,ref , computed} from 'vue'
import { getCategoryList } from '../api'
import BScroll from '@better-scroll/core'
const menus = ref([])
const rightLiTops = ref([])
const menuList = ref()
let leftBscroll = null
const scrollY = ref(0) // 右侧列表滑动的 y 轴坐标
let rightBscroll = null
const itemList = ref()
onMounted(() => {
 loadCategoryList()
 RightHeightFix()
})
// 监听
watch(menus, () => {
 nextTick(() => {
  initBScroll()
 initRightHeight()
 })
})
// 获取分类数据
const loadCategoryList = async () => {
 let data = await getCategoryList()
  // 将一维数组数据转换为树形结构
 const treeData = convertToTree(data)
 // 将转换后的数据赋值给 menus
 menus.value = treeData
}
// 将一维数组转换成树形结构的方法
const convertToTree = data => {
 const treeData = []
 const map = {}
 // 遍历一维数组数据，建立节点映射表
 for (const item of data) {
 map[item.id] = { ...item, children: [] }
 }
 // 遍历映射表，将节点添加到父节点的 children 中
 for (const item of data) {
 const node = map[item.id]
 if (item.pid === 0) {
 treeData.push(node)
 } else {
 const parent = map[item.pid]
 parent.children.push(node)
 }
 }
 return treeData
}
// 单击左侧菜单项
const clickList = index => {
  scrollY.value = rightLiTops.value[index]
 rightBscroll.scrollTo(0, -scrollY.value)
}
// 初始化右边菜单的高度
const initRightHeight = () => {
 const itemArray = []
 let top = 0
 itemArray.push(top)
 const allList = itemList.value.getElementsByClassName('cate')
 Array.prototype.slice.call(allList).forEach(li => {
 top += li.clientHeight
 itemArray.push(top)
 })
 rightLiTops.value = itemArray
}
// 初始化 BScroll
const initBScroll = () => {
 // 初始化左菜单
 leftBscroll = new BScroll('.menu-left', {
 click: true,
 mouseWheel: true
 })
 // 初始化右菜单
 rightBscroll = new BScroll('.menu-right', {
 click: true,
 mouseWheel: true,
 probeType: 3 // 实时派发 scroll 事件
 })
 rightBscroll.on('scroll', pos => {
 scrollY.value = Math.abs(pos.y)
 })
}
const RightHeightFix = () => {
 let bottom = itemList.value.getElementsByClassName('cate-bottom')[0]
 bottom.style.height = itemList.value.clientHeight / 1.2 + 'px'
}
const initLeftScroll = index => {
 const menu = menuList.value
 let el = menu[index]
 leftBscroll.scrollToElement(el, 300, 0, -100)
}
const currentIndex = computed(() => {
 return rightLiTops.value.findIndex((top, index) => {
 if (index === rightLiTops.value.length - 2) {
 return true
 }
 if (scrollY.value >= top && scrollY.value < rightLiTops.value[index +
1]) {
 initLeftScroll(index)
 return true
 }
 })
})
</script>
<template>
  <div class="menu">
  <div class="menu-left">
  <ul>
  <li class="menu-item" v-for="(menu, index) in menus" :key="index"  :class="{ current: index === currentIndex }" @click="clickList(index)" ref="menuList">
  <p class="text">{{ menu.name }}</p>
  </li>
  </ul>
  </div>
  <div class="menu-right" ref="itemList">
  <!-- 显示二级分类 -->
  <ul>
  <li class="cate" v-for="(menu, index1) in menus" :key="index1">
  <h4 class="cate-title">{{ menu.name }}</h4>
  <ul class="cate-item">
  <li v-for="(item, index2) in menu.children" :key="index2">
  <router-link class="cate-item-wrapper" :to="{ name: 'goodslist', params:{ category_id: item.id } }">
  <div class="cate-item-img">
  <img :src="item.picture" alt="">
  </div>
  <span>{{ item.name }}</span>
  </router-link>
  </li>
  </ul>
  </li>
  <li class="cate-bottom"></li>
  </ul>
  </div>
  </div>
 </template>
 <style lang="less" scoped>
 ul {
  margin: 0;
  padding: 0;
 }
 li {
  list-style: none;
 }
 .menu {
  display: flex;
  position: absolute;
  text-align: center;
  top: 46px;
  bottom: 50px;
  width: 100%;
  overflow: hidden;
  .menu-left {
  flex: 0 0 80px;
  width: 80px;
  background: #f3f5f7;
  line-height: 54px;
  .menu-item {
  height: 54px;
  width: 100%;
  border-bottom: 1px solid #e1e1e1;
  .text {
  width: 100%;
  margin: 0;
  }
  }
  .current {
  width: 100%;
  background: #fff;
  .text {
  color: red;
  }
  }
  }
  .menu-right {
  flex: 1;
  background: #fff;
  .cate {
  height: 100%;
  .cate-title {
  margin: 0;
  text-align: left;
  font-size: 14px;
  color: #333;
  font-weight: bold;
  padding: 10px;
  }
  .cate-item {
  padding: 7px 10px 10px;
  display: flex;
  overflow: hidden;
  flex-flow: row wrap;
  li {
  width: 33.3%;
  .cate-item-wrapper {
  .cate-item-img {
  width: 100%;
  img {
  width: 70px;
  height: 70px;
  }
  }
  span {
  display: inline-block;
  font-size: 14px;
  color: #333;
  }
  }
  }
  }
  }
  }
 }
 </style>